"To kill him right away would not have achieved that result."
Exactly, terrorism's goal is to produce terror and to assume control over the terrorised, the desired result is not simply dead bodies.
But it does seem that the "successful" terrorist has the highest body counts. Why else would 9/11 be hailed as such a heroic feat in islamic countries (and on some American college campuses)?
And what of the terrorists' own voiced desire to see as many Americans dead as they can kill?